rsa/*: switch to BN_bn2binpad.

Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5254)

crypto/rsa/rsa_oaep.c

@@ -150,32 +150,40 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 
     dblen = num - mdlen - 1;
     db = OPENSSL_malloc(dblen);
-    em = OPENSSL_malloc(num);
-    if (db == NULL || em == NULL) {
+    if (db == NULL) {
         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
         goto cleanup;
     }
 
-    /*
-     * Always do this zero-padding copy (even when num == flen) to avoid
-     * leaking that information. The copy still leaks some side-channel
-     * information, but it's impossible to have a fixed  memory access
-     * pattern since we can't read out of the bounds of |from|.
-     *
-     * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
-     */
-    memset(em, 0, num);
-    memcpy(em + num - flen, from, flen);
+    if (flen != num) {
+        em = OPENSSL_zalloc(num);
+        if (em == NULL) {
+            RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
+                   ERR_R_MALLOC_FAILURE);
+            goto cleanup;
+        }
+
+        /*
+         * Caller is encouraged to pass zero-padded message created with
+         * BN_bn2binpad, but if it doesn't, we do this zero-padding copy
+         * to avoid leaking that information. The copy still leaks some
+         * side-channel information, but it's impossible to have a fixed
+         * memory access pattern since we can't read out of the bounds of
+         * |from|.
+         */
+        memcpy(em + num - flen, from, flen);
+        from = em;
+    }
 
     /*
      * The first byte must be zero, however we must not leak if this is
      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
      */
-    good = constant_time_is_zero(em[0]);
+    good = constant_time_is_zero(from[0]);
 
-    maskedseed = em + 1;
-    maskeddb = em + 1 + mdlen;
+    maskedseed = from + 1;
+    maskeddb = from + 1 + mdlen;
 
     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
         goto cleanup;

crypto/rsa/rsa_ossl.c

@@ -68,7 +68,7 @@ static int rsa_ossl_public_encrypt(int flen, const unsigned char *from,
                                   unsigned char *to, RSA *rsa, int padding)
 {
     BIGNUM *f, *ret;
-    int i, j, k, num = 0, r = -1;
+    int i, num = 0, r = -1;
     unsigned char *buf = NULL;
     BN_CTX *ctx = NULL;
 
@@ -142,15 +142,10 @@ static int rsa_ossl_public_encrypt(int flen, const unsigned char *from,
         goto err;
 
     /*
-     * put in leading 0 bytes if the number is less than the length of the
-     * modulus
+     * BN_bn2binpad puts in leading 0 bytes if the number is less than
+     * the length of the modulus.
      */
-    j = BN_num_bytes(ret);
-    i = BN_bn2bin(ret, &(to[num - j]));
-    for (k = 0; k < (num - i); k++)
-        to[k] = 0;
-
-    r = num;
+    r = BN_bn2binpad(ret, to, num);
  err:
     if (ctx != NULL)
         BN_CTX_end(ctx);
@@ -239,7 +234,7 @@ static int rsa_ossl_private_encrypt(int flen, const unsigned char *from,
                                    unsigned char *to, RSA *rsa, int padding)
 {
     BIGNUM *f, *ret, *res;
-    int i, j, k, num = 0, r = -1;
+    int i, num = 0, r = -1;
     unsigned char *buf = NULL;
     BN_CTX *ctx = NULL;
     int local_blinding = 0;
@@ -354,15 +349,10 @@ static int rsa_ossl_private_encrypt(int flen, const unsigned char *from,
     }
 
     /*
-     * put in leading 0 bytes if the number is less than the length of the
-     * modulus
+     * BN_bn2binpad puts in leading 0 bytes if the number is less than
+     * the length of the modulus.
      */
-    j = BN_num_bytes(res);
-    i = BN_bn2bin(res, &(to[num - j]));
-    for (k = 0; k < (num - i); k++)
-        to[k] = 0;
-
-    r = num;
+    r = BN_bn2binpad(res, to, num);
  err:
     if (ctx != NULL)
         BN_CTX_end(ctx);
@@ -376,7 +366,6 @@ static int rsa_ossl_private_decrypt(int flen, const unsigned char *from,
 {
     BIGNUM *f, *ret;
     int j, num = 0, r = -1;
-    unsigned char *p;
     unsigned char *buf = NULL;
     BN_CTX *ctx = NULL;
     int local_blinding = 0;
@@ -472,8 +461,7 @@ static int rsa_ossl_private_decrypt(int flen, const unsigned char *from,
         if (!rsa_blinding_invert(blinding, ret, unblind, ctx))
             goto err;
 
-    p = buf;
-    j = BN_bn2bin(ret, p);      /* j is only used with no-padding mode */
+    j = BN_bn2binpad(ret, buf, num);
 
     switch (padding) {
     case RSA_PKCS1_PADDING:
@@ -486,7 +474,7 @@ static int rsa_ossl_private_decrypt(int flen, const unsigned char *from,
         r = RSA_padding_check_SSLv23(to, num, buf, j, num);
         break;
     case RSA_NO_PADDING:
-        r = RSA_padding_check_none(to, num, buf, j, num);
+        memcpy(to, buf, (r = j));
         break;
     default:
         RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
@@ -509,7 +497,6 @@ static int rsa_ossl_public_decrypt(int flen, const unsigned char *from,
 {
     BIGNUM *f, *ret;
     int i, num = 0, r = -1;
-    unsigned char *p;
     unsigned char *buf = NULL;
     BN_CTX *ctx = NULL;
 
@@ -574,8 +561,7 @@ static int rsa_ossl_public_decrypt(int flen, const unsigned char *from,
         if (!BN_sub(ret, rsa->n, ret))
             goto err;
 
-    p = buf;
-    i = BN_bn2bin(ret, p);
+    i = BN_bn2binpad(ret, buf, num);
 
     switch (padding) {
     case RSA_PKCS1_PADDING:
@@ -585,7 +571,7 @@ static int rsa_ossl_public_decrypt(int flen, const unsigned char *from,
         r = RSA_padding_check_X931(to, num, buf, i, num);
         break;
     case RSA_NO_PADDING:
-        r = RSA_padding_check_none(to, num, buf, i, num);
+        memcpy(to, buf, (r = i));
         break;
     default:
         RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT, RSA_R_UNKNOWN_PADDING_TYPE);

crypto/rsa/rsa_pk1.c

@@ -175,27 +175,30 @@ int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
     if (num < 11)
         goto err;
 
-    em = OPENSSL_zalloc(num);
-    if (em == NULL) {
-        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
-        return -1;
+    if (flen != num) {
+        em = OPENSSL_zalloc(num);
+        if (em == NULL) {
+            RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
+            return -1;
+        }
+        /*
+         * Caller is encouraged to pass zero-padded message created with
+         * BN_bn2binpad, but if it doesn't, we do this zero-padding copy
+         * to avoid leaking that information. The copy still leaks some
+         * side-channel information, but it's impossible to have a fixed
+         * memory access pattern since we can't read out of the bounds of
+         * |from|.
+         */
+        memcpy(em + num - flen, from, flen);
+        from = em;
     }
-    /*
-     * Always do this zero-padding copy (even when num == flen) to avoid
-     * leaking that information. The copy still leaks some side-channel
-     * information, but it's impossible to have a fixed memory access
-     * pattern since we can't read out of the bounds of |from|.
-     *
-     * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
-     */
-    memcpy(em + num - flen, from, flen);
 
-    good = constant_time_is_zero(em[0]);
-    good &= constant_time_eq(em[1], 2);
+    good = constant_time_is_zero(from[0]);
+    good &= constant_time_eq(from[1], 2);
 
     found_zero_byte = 0;
     for (i = 2; i < num; i++) {
-        unsigned int equals0 = constant_time_is_zero(em[i]);
+        unsigned int equals0 = constant_time_is_zero(from[i]);
         zero_index =
             constant_time_select_int(~found_zero_byte & equals0, i,
                                      zero_index);
@@ -203,7 +206,7 @@ int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
     }
 
     /*
-     * PS must be at least 8 bytes long, and it starts two bytes into |em|.
+     * PS must be at least 8 bytes long, and it starts two bytes into |from|.
      * If we never found a 0-byte, then |zero_index| is 0 and the check
      * also fails.
      */
@@ -232,7 +235,7 @@ int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
         goto err;
     }
 
-    memcpy(to, em + msg_index, mlen);
+    memcpy(to, from + msg_index, mlen);
 
  err:
     OPENSSL_clear_free(em, num);

crypto/rsa/rsa_ssl.c

@@ -63,6 +63,14 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
         RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
         return -1;
     }
+    /* Accept even zero-padded input */
+    if (flen == num) {
+        if (*(p++) != 0) {
+            RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_BLOCK_TYPE_IS_NOT_02);
+            return -1;
+        }
+        flen--;
+    }
     if ((num != (flen + 1)) || (*(p++) != 02)) {
         RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_BLOCK_TYPE_IS_NOT_02);
         return -1;